A/N: I love this pairing! I was so gutted when JK didn't put it in the book, but when I saw the film it completely made up for it!
Disclaimer: Obviously I don't own Harry Potter
Set some time throughout their lives together really, I like to think they're engaged/married by the end of it but it's not really got a plot to it, just a description. So yes, sometime around 6th year/7th year and beyond then.
The Progressions of a Friendship
They started out as friends, acquaintances even. They'd meet up every so often, accidentally of course, never planned, and she'd teach him some nonsense about Blibbering Humdingers or something just as crazy and he'd listen. After she'd finished, he would teach her something real, something that made sense, but he listened to her side just as enthusiastically. He found her complete loyalty in the existence of Nargles and Wrackspurts fascinating; to him, her ability to stand by her beliefs no matter how many times people disputed them was admirable and he longed to have the ability to shut himself away from the cynicism, like she managed to do every single day. He soon found himself longing for her company too.
Overnight, they became best friends; it was the first true best friend either of them had ever had and something that both of them had been craving for some time, without even realising it. She'd just turned to him one day and said: "You know you're my best friend don't you?" And that was that. They met every week without fail by the lake on a Saturday for a walk and she'd sit by him at the Gryffindor table at most of the meals, when either of them stopped to think about it there wasn't a lot of time when they weren't together. Both seemed quite content at being each others best friends.
In 7th year, when everything suddenly went wrong, she was taken away from him. That's when he realised there was something different about his feelings towards his best friend. His tummy churned whenever he thought about her with Bellatrix, when he thought of them hurting her; he'd give his own life to have her safe, he'd give anything to have her back by his side. He couldn't quite put his finger on the change in his feelings, all he knew was that whenever he was being tortured he just had to imagine her smile and he'd be fine, whenever he couldn't sleep her face would fill his mind and he'd be off into dreams of her within minutes. His hopes of seeing her again were the only thing that got him through.
She'd noticed the change in feelings too, when she was locked in Malfoy Manor. Usually, when she let her thoughts wander she'd think about how there were an awful lot of Nargles around or something as equal to that, but she found that now all she ever thought about was him. He was the closest thing she'd ever got to a boyfriend: he hugged her, listened to her and he'd even let her fall asleep on him once outside in the sun, that had been one of the happiest days she'd had. Of course her being her, she'd never really noticed until she was as far away from him as possible. She yearned for him. Then he had marched up to her, in the middle of the war, and confessed how much he loved her and all of a sudden she found herself kissing him, in the middle of all the jinxes and curses they just stood there, wrapped up in each other. It was perfect.
After that the war was over, Voldemort was dead and his own act of bravery was a key part in bringing the Wizarding World to peace, he couldn't help but feel proud of himself. Then he saw her again, for the first time after his mad confession, after he'd finally realised why his feelings for his eccentric, intriguing, beautiful best friend actually were. He loved her. It was simple. Everything about her amazed him: he loved the way her hair was so long, he loved the way it blew in the wind, he loved the way her eyes shone constantly for no apparent reason and he loved how the ends of her lips were always slightly lifted in a never ending smile. Everything about her was perfect.
After their realisations, they didn't leave each others sides, she had no one she'd rather be with and neither did he and they learnt to love different things about each other. She loved how cautious he was when he helped to tend to her wounds, she loved how he snuck her into the Gryffindor dormitories (though just after the war no one really cared anyway) and they laid there together and slowly fell asleep, she loved how proud he was to call her his girl friend. No one but her father and mother had ever been as proud of her as he was.
He loved how she decorated their first house together with bright colours like purple and turquoise because apparently Wrackspurts weren't particularly fond of them, he loved how she called him Nevvy, it was slightly cheesy but it was the first nickname he'd ever had and she'd given it to him so it was wonderful, and most of all he loved her name. It was the first thing he thought of whenever anybody asked him what he loved about her. He'd always thought it was such a musical name, it slipped of people's tongues like a poem, the alliteration made it sound magical, just like she was. Luna Lovegood. Perfect.
But then again, he'd always thought Luna Longbottom had quite a nice ring to it too.